The present invention relates to a panel substrate, a display panel, an organic EL (Electroluminescence) panel, and a method of manufacturing the organic EL panel.
The present application claims priority from Japanese Applications Nos. 2004-76087, 2004-34656, the disclosures of which are incorporated herein by reference.
A flat display panel is usually formed by mounting at least one display (element) device on a panel substrate, and it has been pointed out that a flatness of the surface of such a panel substrate greatly affects the displaying performance of the display panel. Especially, with regard to an organic EL panel, if there are irregularities on the surface of a panel substrate, an un-uniformity will occur in the thickness of each of several layers laminated on the panel substrate, resulting in a deteriorated displaying performance.
FIG. 1 is a sectional view showing the cross section of an organic EL (element) device 10 for use in forming a conventional organic EL panel. As shown, the organic EL device 10 mounted on a panel substrate 11 has a laminated structure formed by interposing an organic layer 20 containing at least one organic luminescence layer between a pair of electrodes. Further, insulating films 13 are formed around a lower electrode 12 on the panel substrate 11, while an area on the lower electrode 12 surrounded by the insulating film 13 forms a luminescent area S. Moreover, in the luminescent area S, the organic layer 20 is laminated on the lower electrode 12, while an upper electrode 14 is formed on the organic layer 20.
As one example, the organic layer 20 has a three-layer structure including a hole transporting layer 21, a luminescent layer 22, and an electron transporting layer 23, with the lower electrode 12 serving as an anode and the upper electrode 14 as a cathode. However, it is also possible to form a structure not including the hole transporting layer 21 and/or the electron transporting layer 23, or a structure in which at least one of the aforementioned layers is formed into a multi-layered structure. Alternatively, it is also possible to form a hole injection layer on the anode side of the hole transporting layer 21, and an electron injection layer on the cathode side of the electron transporting layer 23. In addition, it is further possible for the lower electrode 12 to be used as a cathode and the upper electrode 14 as an anode.
Such an organic EL device for use in forming an organic EL panel, once under an electric voltage applied between the lower electrode 12 and the upper electrode 14, allows positive holes to be injected and transported from the anode side to the organic layer 20, and electrons to be injected and transported from the cathode side to the organic layer 20, thereby effecting a light emission through a recombination of the positive-holes with electrons. On such an occasion, although an electric current flows between the anode and the cathode due to the recombination of positive holes with electrons, if there are some surface irregularities on the surface of the panel substrate 11 within the luminescent area S, such surface irregularities will also occur on the surface of the lower electrode 12 mounted on the panel substrate 11. As a result, some thin portions will locally occur in the organic layer 20 within the luminescent area S. Once such thin portions locally occur, a leak current (different from the current caused by the aforementioned recombination) will be generated there, causing some problems such as an emission failure and an increased power consumption.
In order to solve the above problem, Japanese Unexamined Patent Application Publication No. 11-191487 suggests that the surface flatness of a panel substrate can be improved if the surface thereof is polished chemically or mechanically prior to forming an organic EL device on the panel substrate.
With regard to the aforementioned conventional polishing method for treating the surface of a panel substrate, although it is possible to easily shave convexities on such surface, it is impossible to eliminate some scratches-like deep concavities without cutting a thick portion from the surface of the panel substrate. Actually, since the depths of such concavities are unrecognizable, it is difficult to completely eliminate such concavities on the panel substrate surface.
Usually, two kinds of glass substrates have been utilized as a panel substrate for a flat panel display, one is called “soda lime glass” if containing an alkaline component, and the other “non alkaline glass” if not containing an alkaline component. When utilizing a panel substrate containing an inexpensive alkaline component, a commonly used method is to coat the surface of the panel substrate with an SiO2 film through sputtering, thereby preventing an undesired effect of the alkaline component of the panel substrate on the above-mentioned display (element) device.
However, with regard to the aforementioned panel substrate surface on which the concavities are still remaining, even if the SiO2 film has been formed through sputtering, it is still impossible for a sputtering process to provide a thick film because of the necessity of film-stress control, hence making it impossible to fill the concavities on the panel substrate surface. In addition, since pin-holes of the SiO2 film will be formed in these concavities, it is impossible to block an invasion of the alkaline component of the panel substrate even if the SiO2 film has been formed.